Current production printing utilizes known techniques, such as two-dimensional (2D) printing technology, to print image content on objects. In order to print customized image content on a portion of 3D object, the printheads have to be maneuvered to present the object portion to be printed as a parallel plane to the printheads. Additionally, curved or irregular surfaces are difficult to print with a plane of printheads because the gap between the ejectors in the printheads and the surface of the object differ with reference to the curvature or elevation changes in the surface. The differences in gaps between the ejectors and the surface can be enough to affect the registration of the printing since some drops of material travel further than other drops of material. Consequently, air turbulence can affect the movement of the drops that travel further or the ejector can be slightly angled in the printhead. This latter defect is not as noticeable for drops travelling shorter distances than it is for drops travelling longer distances. Also, the shape of a drop of ink varies as it moves through the gap between a printhead and a part. Consequently, gap size can affect whether a drop is properly shaped, forms a satellite drop, is improperly shaped, or becomes multiple drops as it lands on the object. These and other known effects prevent many objects, particularly curved or irregular objects, from being printed by previously known printers.
Transfer printing of three-dimensional objects with photo-resist materials has been tried. In these previously known systems, an image is printed on a sheet with photo-resist materials that are curable with ultraviolet (UV) radiation. The sheet is then placed against the surface of the object and then pressed against the object or vacuum is applied between the sheet and the object to draw the sheet against the object. The back of the sheet is radiated with UV radiation to cure the photo-resist material. When the sheet is removed from the object, the photo-resist remains on the object surface and the surface can then be etched to form the pattern in the surface of the object. Alternatively, the photo-resist pattern on the object surface can act as a plating resist to preserve the covered areas when the object is plated. Afterwards, the photo-resist material is removed.
This approach uses UV radiation to transfer the photo-resist image to the object because heat and pressure transfer of an image from a sheet fails to register the image appropriately on the surface. Waiting until the sheet is in contact with the object surface, however, requires the use of particular types of ink to avoid ink movement or uncured ink mixing before the sheet contacts the object surface. For example, differences in surface energy between drops of UV curable inks and the surface on which they land can cause the drops to move after they have landed. This movement can produce holes in areas where the coverage is supposed to be continuous or cause drops of different colors to mix and form unintended colors that can adversely impact the quality of the image. To address these issues, the previously known 3D object printing systems used UV inks that have a high enough percentage of wax in the ink that the ink is solid at room temperature. By melting the ink and ejecting it to form a photo-resist pattern, the pattern stabilizes as it cools, which commences as soon as the ink is ejected. Being able to use UV inks that do not have to be solid at room temperature would be useful.
Other transfer image systems use sheets pre-printed with dye inks to avoid the issues related to ink movement and color mixing. The pre-printed sheets having fixed images on them, however, require that the sheets be heated once the sheet is applied to the object surface to release the fixed ink image from the sheet so it can be transferred by pressure. This type of previously known system requires that the image sheet preparation be a separate process from the object printing since the image must be fixed on the sheet so the sheet can be manipulated and conform to the object surface for image release. Thus, a printer that enables reliable printing of curved 3D object surfaces using a broad array of inks without requiring a separate image sheet printing process is desirable.